1. Field of the Invention
The present invention relates generally to signal measurement systems and, more particularly, to invoking measurements in signal measurement systems.
2. Related Art
Conventional signal measurement systems such as digital oscilloscopes sample, record and display time-varying analog signals. Samples of an input signal are taken and quantized, and the resultant digital representations are stored in a waveform memory under the control of a sampling clock. The acquired data may subsequently be read out as locations in memory are sequentially addressed by a clock signal to provide digital data which can be converted to a time-varying output signal for a waveform display. The sampling clock may be operated at one of several selectable rates depending upon the frequency content of the input signal. The selection of the portion of the analog input signal which is sampled and stored is determined by appropriate triggering circuitry to enable the operator to display the desired portion of the waveform.
There are many types of display elements which can be presented in signal measurement systems in general and test and measurement instruments in particular. For example, in addition to the waveforms representing the signals currently received at the channel inputs, waveforms referred to as function waveforms may also be displayed. Function waveforms are waveforms created by processing the signal waveforms. Such processing may include, for example, performing arithmetic manipulations on a signal waveform or combining multiple input signal waveforms in some predetermined manner. The resulting waveforms are placed in a display memory for subsequent retrieval and display. In addition, memory waveforms may also be displayed. Memory waveforms are waveforms which have been stored in memory. In addition to the above waveforms, other display elements such as marker indicators, trigger indicators, etc. are typically displayed.
A primary function provided by signal measurement systems in the analysis of signals is to perform automated measurement of desired signal parameters. Automated measurements allow a user to quickly and accurately determine key parameters of acquired signals without the use of manual calculations. Furthermore, automated measurements are a useful and productive technique for characterizing electrical signals using common, well-understood quantities such as peak-to-peak voltage, rise time and frequency. In addition, automated measurements are often used to verify that a given circuit or hardware component satisfies established performance specifications.
To perform an automated measurement in conventional signal measurement systems, a number of actions are typically required to be performed by the user. The desired measurement must be selected and the waveform source for the measurement must be identified. In addition to associating the selected measurement with a source waveform, additional information may need to be specified including, for example, the portion or extent of the selected waveform over which the measurement is to be applied.
Conventional techniques for invoking oscilloscope measurements often involve the use of push-button keys on the instrument's front panel. A measurement is selected by depressing a dedicated key with the associated measurement's name printed on or above it. A source waveform is subsequently identified either by pressing a key associated with a particular channel or other signal or by turning a knob that scrolls through a list of possible sources.
In another conventional approach, the desired measurement is selected by pressing a multifunction `softkey` whose current function is to invoke a given measurement. Typically, the softkey is located near a textual or graphical display of the key's current function. With this approach, the current function of the softkey must first be assigned through the activation of a `menu` or `setup` key. The menu/setup key may be a fixed function key located on the front panel, or may itself be a softkey whose current function is to assign functions to one or more softkeys. In these conventional systems source waveform selection is typically accomplished with still additional softkey operations. In other conventional instruments a hybrid solution is sometimes employed. For example, measurement selection is accomplished with fixed functions keys, while source waveform selection is performed using softkeys.
As noted, in addition to selecting the measurement and source waveform oftentimes a specific region of the selected waveform on which the measurement is to be applied must be selected by the user. For such measurements, the desired horizontal extent of the selected waveform should be selected for measurement. For example, an individual pulse among a series of pulses may need to be selected to measure the period of the signal. Conventional signal measurement systems employ several different methods to select specific waveform regions. In one conventional approach, such measurements are applied to the first cycle of the waveform on the displayed waveform beginning with the left-most pulse. In these systems, the horizontal position controls must be adjusted by the user so that the pulse of interest appears at the left-most position on the waveform display.
In other conventional approaches a set of marker indicators (visual lines with adjustable vertical and horizontal positions) must be activated and positioned such that the markers bound the region of the signal to be measured. Yet another approach requires the user to enter a numeric value to specify the number of the pulse of interest relative to the total number of pulses displayed. Another approach is to eliminate the need for region selection by adjusting both horizontal scale and position and perhaps the trigger specification such that only the single pulse of interest appears on the waveform display.
There are a number of drawbacks to these conventional approaches. First, these conventional techniques require multiple key presses and/or knob turns to be carried out in a specified sequence in order to properly invoke a measurement. Not only is such an arrangement difficult to understand and operate, considerable time is consumed performing the requisite steps to obtain a desired measurement. This is particularly the case when a number of measurements are to be performed on different regions of one or more waveforms. To perform such a series of measurements in conventional systems, very complex procedures must be performed to successively select particular regions of the waveform, resulting in a system which is difficult for the novice or infrequent user to operate and understand.
Moreover, the requirement to select a region or horizontal extent often places additional sequencing constraints on the overall invocation process. Common to many implementations of conventional systems is the requirement that the region identification must be performed prior to selection of the measurement. Thus, these conventional approaches require both the waveform and waveform region to be selected prior to the selection of the waveform. This is often counterintuitive to the typical user who most often wants to choose the measurement first, then apply the measurement to a certain part of a certain signal.
A further drawback to these conventional approaches is the limited indications provided to the user with instructions and feedback. For example, certain measurements are only applicable to certain types of waveforms. No indication is provided to notify a user that an attempt to apply a measurement to a waveform is incorrect. As a result, the user may navigate through a significant series of softkey layers to select the source waveform, manipulate various knobs to identify the region to measure, and then again navigate among a series of softkeys to select the measurement. It is not until after these operations are performed that a determination is made and the user is informed of the incorrect assignment, causing the user to repeat a significant number of procedural steps to invoke a proper measurement.
What is needed, therefore, is a simple, intuitive means for performing measurements on waveforms which does not erect a productivity barrier that hinders more widespread use of automated measurement functions.